He couldn't e here.Something happened
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选Asth.happen to sb.某人发生了某事
例：What happened to you yesterday?你昨天怎么了?
题中的这句话是说“他没能来.昨天他有点什么事.”
另外happen to 也表示偶然性,突然性
例：I happened to find that he was my former neighbour.我忽然发现他是我从前的邻居.
======以下答案可供参考======
供参考答案1:
选A供参考答案2:
A供参考答案3:
选A